New Speakers under consideration - but I’m afraid

Well a 15k speaker today there 15 yo equivalent would be about 4k back then.

That’s adjusted for inflation, but does that also apply to or account for the potential for increased performance due to R&D over 25 years?

If you like the B&W sound you are on the right track with the options you mention but you might like to add Focal to the list. Not my cup of tea but speaker choice is very personal and I prefer the more musical (less analytical ) speakers like Sonus Faber.

Why not stay with what you have? They are excellent speakers

Listening to music in the Bahamas on any of the speakers on your list sounds divine to me.

The 801s were $5.5k in 1999. New.
 

Several years ago I took a fav cd and went and listened to WW Puppies driven by great electronics and thought what’s the big deal. They did not seem to resolve any better and seemed lacking on the bottom. 
 

Now, how many iterations later, I wonder if the Sashas have improved enough- surely they must have, no? I would be looking at used so listening may be an issue.

The new 802s ( I wrote 803s above but meant 802s) share the same B&W DNA so should be an improvement and safer choice (but would still go for a listen). My ears have rolled off on top so B&W brightness may be less of an issue. 
 

I’m a big believer in physics and can’t see (or hear) how the X3s go very deep, but I failed to mention that I have a VMPS Larger sub driven by Crown K2, so deep bass is not an issue. Will try and have listen in Fla.